This invention relates to improved golf club shafts and methods of manufacturing golf club shafts.
The shaft is the most important part of a golf club. It couples the golfer to the club head by which the golfer strikes the ball and is the primary component by which the golfer can manipulate the club head in executing the shot which he has planned. The playability of a golf club and its "feel" (that is, the ability of the golf club to reproduce the shot intended by the golfer and to instill confidence in the golfer through his kinesthetic senses that he can produce the intended shot) are primarily attributable to the shaft of a golf club.
In the backswing of a golfer, the golf club is accelerated and moved rather slowly to the top of the golfer's backswing; and the golf club shaft flexes insignificantly but should transmit the feel of the club head to the golfer through the golfer's grip at the end of the shaft. As the golfer executes his shot from the top of the backswing, however, the golf club shaft experiences first the flexural and torsional forces imposed on the golf shaft by the high acceleration and the offset weight of the club head, and then the further and abrupt imposition of flexural and torsional forces as the club head strikes the stationary ball and frequently the ground from which the ball is played. The complex forces imposed on the club shaft are further complicated by the variety of terrain on which golf is played. The terrain of some golf courses is soft, lush grass growing on well-watered and soft earth. On other golf courses, however, the grass may be thin and sparse and growing on hardened clay. Still other courses may be built on a sandy or loamy soil. Each of these different playing conditions imposes different forces in the golf club shaft as the golfer hits the ball from the surface of the course. In addition, the golf club shaft must frequently be used to play the ball from dense, heavy vegetation which is allowed to grow off the fairway of a golf course, or from the sand of traps. Under all these varying conditions, it is desirable for the golfer be confident that his golf club is playable to produce the shot he intends.
As a result of the forces imposed on a golf club during a shot, the golf club shaft bends along its longitudinal axis and twists somewhat as the golfer swings the club from the top of his backswing at the ball. Because of the resiliency of the golf club shaft, the bending and twisting of the shaft, due to its rapid acceleration at the top of the backswing, will be released; and the period of this release (the timing of the recovery of the bending) is an important factor in the consistency with which a golfer may hit the ball and the playability and feel of the club. In addition, the golf club shaft stores energy during the bending of the shaft as the golfer accelerates the club from the top of his backswing; and this energy may be returned to the ball as it is struck if the resiliency of the golf club shaft can be timed by the golfer to return the golf club shaft to its original straight position as the club head strikes the ball. The return of energy by the golf club shaft to the head of the club and the golfer's ability to time his swing to take advantage of that return of energy are two factors which can produce distance in the travel of the golf ball; and the ability to hit a golf ball long distances, when desired, is always advantageous in the game of golf. This, of course, means the golf club shaft, for best results, should be capable of matching the period of release of energy stored by flexure with the natural tempo of the golf swing of the golfer using the club.
Torsional deflection of the shaft and the release of energy stored as a result of such torsional deflection, while it may theoretically contribute a small additional energy to the golf ball and contribute to the distance of the resulting shot, are generally undesirable because the possible angular deflection of the face of the club from the intended line of flight introduces a source of angular error in the intended flight of the golf ball which is hardly ever desirable.
It is important and desirable to minimize the weight of the golf club shaft to the extent possible and consistent with providing the golf club shaft with the desired flexural characteristics. It is also important that the golf club as a whole not weigh too much and that it feels easily manipulatable in the hands of the golfer. For maximum energy transfer from the golf club to the ball, it is desirable that the maximum amount of the weight of the golf club be concentrated immediately behind the ball, i.e., at the face of the golf club, as the club moves through the ball. Thus, concentration of a high portion of the weight of the golf club behind the face of the ball, release of the energy stored in the golf club shaft as the ball leaves the face of the golf club, and minimum angular deflection from the original position of the golf club face are desirable properties to be obtained in a golf club and as a result of the use of a most desired golf club shaft.
The population of golfers, of course, is almost infinite in its variety of age, strength, suppleness, athletic ability, physical coordination, hand/eye coordination, kinesthetic sensitivity, ability to concentrate, and ability to execute golf shots. Thus, some golfers rely heavily upon their strength; some rely upon their suppleness and coordination; still others have a natural combination of strength, suppleness, coordination and ability to execute a golf shot; and, of course, many golfers have a poor ability to play golf. Because of the almost infinite variety of physical differences and abilities of golfers, an almost infinite variety of golf club shafts may be used to provide golfers with the best marriage between their abilities to swing the club and the ability of the golf club to produce a reproducible and intended golf shot.
It is not possible, of course, for a golf club manufacturer to inventory the almost infinite variety of golf club shafts needed to satisfy this requirement, even for a single club of a set of clubs. The golf club manufacturer's problem is further complicated by an additional variable in the lengths of golf shafts needed to manufacture the multiplicity of clubs that are used in playing golf. The length of a golf club shaft, for example, varies from about forty-two to forty-three inches for a driver's shaft to about thirty- one to thirty-two inches for a pitching iron shaft; and there are anywhere from about twelve to fourteen clubs included within a complete standard set of golf clubs with each of the twelve to fourteen clubs having a shaft of a different length. In addition, the length of the shaft ideally varies with the stature of the golfer, the matching of golf shafts to a golfer's stature being generally determined by the height of a golfer's hands from the surface of the earth on which the golfer stands.
Golf club manufacturers cannot afford to stock the enormous inventory of golf club shafts necessary to satisfy the variety of lengths and flexural characteristics that are needed to produce clubs having the playability and feel suited to the variety of golfers playing the game. In order to minimize the inventory of golf club shafts and reduce the golf manufacturers' investment in such an inventory, golf club manufacturers have frequently adopted five standard flexes for golf club shafts. These five standard flexes are designated generally as extra stiff, stiff, regular, flex, and ladies' grades; and these standard flexes are used both in the carbon steel shafts of the type used in the vast majority of clubs and in the clubs made of fiber/resin composites.
In the manufacture of steel shafts, some effort has been made to control the flex and feel of the shaft by forming the steel shafts with a plurality of linear portions of different diameters; thus, by controlling the diameter of the steel shaft at various portions of its length, the flex of the shaft can be controlled. The deflection of a structural shaft increases as the moment of inertia of its cross section (generally its diameter) decreases. The flexural characteristics of the steel shaft can be only slightly varied by varying the composition of the steel from which the shaft is made. The manufacture of golf club shafts from resin/fiber composites offers a greater opportunity to vary the flexural characteristics of the shaft and provides, generally, a lighter shaft.
There have been substantial prior efforts to solve the inventory problem and provide a golf club shaft that may be suited to a variety of golfers. Examples of patents directed to such prior efforts include: U.S. Pat. Nos. 1,594,801; 2,934,345; 3,313,541; 3,963,236; 4,122,593; 4,240,631; and 4,455,022; and British Pat. No. 1,246,539. Of the above patents, U.S. Pat. Nos. 2,934,345; 3,313,541; and 4,455,022 are directed to golf club shafts including fiberglass. U.S. Pat. Nos. 4,122,593; 4,240,631; 4,455,022; and British specification No. 1,246,539 are directed to a single master golf shaft which may be cut to provide the variable lengths and flexural characteristics to accommodate the variety of golf clubs in a set and the variety of golfers.
These prior efforts, however, have not satisfactorily solved the problem of providing a golf club shaft that permits the variety of lengths and dynamic characteristics that may provide playable sets of golf clubs with good feel to golfers of all abilities and that can reduce the inventory of shafts of golf club manufacturers while permitting the manufacture of golf clubs that can be matched to the stature, strength, swing tempo, physical coordination, and kinesthetic sensitivity of a variety of golfers.